Mumps virus reinfection--clinical findings and serological vagaries.

Sera taken from two cases of mumps reinfection were tested against different strains of mumps virus in a plaque reduction neutralisation assay. Antibodies to mumps in the sera reacted with all strains, but the pattern of emergence of these antibodies differed with the strains tested. These findings raise the possibility of emergence of a mutant strain under the selective pressure of immunisation, with limited or no cross protection induced by the vaccine strain.